A second day of sunshine cheered flagging spirits along the Richelieu River, where some people took advantage of spring floods to explore submerged neighbourhoods...

MONTREAL - Flooding in the Richelieu River has its roots high in the mountains of northern Vermont and New York.

One after another this winter, storms swept over the Adirondacks and the Green Mountains around Lake Champlain, leaving several metres of snow on the ground.

As warmer weather moved into New York and Vermont in March, the snow melted, swelling the 18 rivers and countless streams that empty into Lake Champlain. All across the 21,326 square-kilometre watershed of the lake, water flowed downhill into the lake and the Richelieu River to the north in Quebec.

Then it started to rain. By Friday, water levels in the two bodies of water were at their highest in 140 years.

Like an overflowing bathtub, the water had to go somewhere. It spilled into Mississquoi Bay, flooding shoreline homes and rushed down the Richelieu River, washing over the river banks as it travelled the 124 kilometres to Sorel to empty into the St. Lawrence River.

This spring’s flooding has been called a 100-year-flood, an unprecedented, historic, exceptional event.

“We’ve never seen so much water collect in this lake,” said Bill Howland, manager of the Lake Champlain Basin Program, an agency that works with the Quebec, Vermont and New York governments and local organizations to restore and protect the watershed around Lake Champlain.

Climate change “absolutely” played a role in this spring’s flooding, he said. The number of extreme storms in southern Quebec and the northeastern United States is increasing, something that climate-change models have predicted for the region, Howland said.

“Snow or rain, it’s going to be water coming down and we have to be prepared to deal with it,” he said. “We’ve been seeing signs of this for the past 15 or 20 years.”

A 2010 report by the U.S. Nature Conservancy predicted climate change could lead to an increase in annual precipitation in the Lake Champlain basin, with “heavy storm events” becoming more frequent by the end of the century. Higher precipitation in the watershed – seven per cent of which is in Quebec – could result in Lake Champlain water levels being one to two feet higher by 2100, the report says.

Others say it is too early to know whether climate change had anything to do with this spring’s flooding.

“This happened because of a combination of events,” said Pierre Corbin of Hydro-Météo, which tracks water levels for the province. “We don’t have the evidence to say that there’s a connection with climate change.”

The spring melt happened later than usual this year, and the region around the lake and river got several days of heavy rain in the past two weeks that pushed the water levels even higher, said Robert Leconte, an engineer and hydrologist at the Université de Sherbrooke.

Whether that is a result of climate change isn’t clear, Leconte said. We are at the very beginning of seeing what impacts climate change may have in Quebec, and it’s not clear whether this “exceptional” flooding event can be linked to it, he said.

But it is the kind of extreme weather event that could occur more often than once every 150 years as the climate changes, Leconte said.

The flood waters reached their peak Saturday, and have been slowly receding a few centimetres every day.

Government representatives were to hold a public meeting in St. Basile le Grand Tuesday night to advise people whose homes were flooded about how to return home safely. Similar meetings will be held in other municipalities, said Philippe Jobin, a spokesperson for Quebec’s civil protection agency.

Water levels dropped about four centimetres at St. Jean sur Richelieu and on Lake Champlain Tuesday, and were expected to drop another one to two centimetres overnight, according to Hydro-Météo.

Some of the water is evaporating, some is being used by the plants and trees along the shorelines, and the rest is heading for the St. Lawrence, Howland said.

At this rate, it could be early June before the Richelieu River reaches normal levels, Corbin said.

Only then will the true cost of this spring flooding be known. Buildings, roads and bridges have been damaged, parts of the shoreline have been swept away.

Vermont’s governor has said the cost is at least $3 million in that state alone. The estimated cost in one New York state county is more than $6 million. In Quebec, officials have not said how much it will cost to deal with the flood’s aftermath. The provincial government has already distributed more than $700,000 in flood aid.

Water quality is a major issue. Storm sewers in municipalities along the river are emptying directly into the river instead of going through water-treatment plants. Waves and fast-moving currents have swept away shoreline, dumping dirt, trees, debris and garbage into the lake and river.

“We’ll have to assess it once the water levels are lower, but there are definitely going to be impacts,” said Marcel Comiré of COVABAR, an environmental organization that works on the Richelieu River. “It will be a very big job to evaluate all of that.”

Rushing rivers and streams swept phosphorus, nitrogen and other sediment into Lake Champlain.

“It’s really stirring up the aquatic ecosystems in a very complicated way,” Howland said. “It could be good for some, bad for others.”

Eroded shoreline could mean habitat loss for species that live along the shore. Nesting birds could find their nests and eggs affected, although other species, such as pike, will have much larger wetlands in which to lay their eggs this spring, and mosquitoes should prosper, Howland said.

Generally, though, species that live in and along rivers have adapted to flood conditions because it is a normal occurrence in the spring, said Marc Simoneau, an expert in aquatic environments with Quebec’s Environment Department. There should be little long-term impact to fish, wildlife and plants, he said.

The flooding of houses and streets “is creating safety problems, but this is a completely normal phenomenon for the river,” Simoneau said. “Species that live in and near the river are used to these conditions. They have an ability to survive in that environment.”

Even though the full impact of the flooding won’t be known for weeks, communities along the lake and river can take steps to mitigate the impact, Howland said.

The most important thing is to protect any wetlands because they can hold a lot of water, he said.

Trees and plants can be planted along the edges of the river and lake to help stabilize shorelines to prevent erosion.

Municipalities also have to re-examine construction of their water-treatment plants and drinking water facilities to protect them in case of flooding, Howland added.

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